1. Field
The present disclosure relates generally to the connection of wires to feedthrough pins.
2. Description of the Related Art
Feedthrough pins are frequently used to connect wires to a circuit board. Referring to FIGS. 1 and 2, an exemplary printed circuit board assembly 100 includes a printed circuit board (“PCB”) 102, a plurality of feedthrough pins 104, and a feedthrough 106 (e.g., a ceramic feedthrough) with a plurality of apertures 108 through which the pins extend. The feedthrough pins 104 are arranged in a two-dimensional array with the pins in one row offset from those in the other row and, in the illustrated assembly, the pins are about 0.33 mm in diameter with a space S of about 0.67 mm between adjacent pins. Each feedthrough pin 104 has first and second ends 110 and 112 and a side surface 114 that extends from the first end to the second end. As used herein in the context of a feedthrough pin, an “end” is the surface at the extremity of the pin's length, sometimes referred to herein as an “end surface,” and is not a portion of the side surface. The pins 104 are connected to the associated connection points of the PCB 102 with solder 116, conductive epoxy, or other suitable instrumentalities.
The present inventors have determined that conventional methods of connecting wires to feedthrough pins are susceptible to improvement. This is especially true in those instances where the feedthrough pins are arranged in two-dimensional arrays and/or are arranged in close proximity to one another. Some conventional methods are simply incapable of connecting the wires to feedthrough pins arranged in this manner, while others are labor intensive and expensive. Referring first to FIG. 1, one conventional method of connecting a wire to a feedthrough pin is opposed gap resistance welding, which is a two sided process. Here, the side surface of a pin, a strip of platinum and a wire sandwiched between a pair of welding electrodes as current i passes from one electrode to the other and, accordingly, the electrodes must be able to access opposite sides of the pin. The resistance of the pin, platinum, wire and electrodes produces heat, thereby melting the platinum and bonding the wire to the pin. Although opposed gap resistance welding is a useful technique, the distance between the pins in the above-described closely-spaced two-dimensional array (e.g., the array illustrated in FIGS. 1 and 2) is too small to accommodate both of the electrodes. Spacing notwithstanding, in those instances wherein the portions of the pins 104 above the feedthrough 106 are relatively short, thereby decreasing the thickness of the PCB assembly, it may not be possible to properly position the electrodes on opposite sides of the pin. Similarly, access to the pins is precluded when the pins are recessed within a cavity.
Turning to FIGS. 3 and 4, the present inventors have proposed welding a wire connection terminal 118 to each of the feedthrough pins 104. Each of the terminals 118 includes a cylindrical wall 120, an aperture 122 in which a portion of the associated pin 104 is located, and a slot 124. The present inventors have determined that the process of connecting a wire to a feedthrough pin 104 with a wire connection terminal 118 is relatively labor intensive and expensive. To that end, after the wire connection terminal 118 is welded to the feedthrough pin 104 in a specific orientation, a torch is used to burn the insulation off the end of the wire and the exposed conductor is placed into the slot 124. Tweezers are then used to compress the connection terminal 118 and close the slot 124, thereby crimping the wire to the feedthrough pin 104. In addition to labor, the cost of a platinum terminal is about $10, and there can be many pins and terminals in a device. In addition to being relatively labor intensive and expensive, the manual crimping process can lead to inconsistent pull-strength of the connection. The terminals also effectively reduce the spacing between adjacent feedthrough pins 104 and increase the likelihood that an exposed portion of a wire associated with one pin will contact another pin (by way of that pin's connection terminal) and cause a short.